Mitochondrial Fission in Huntington's Disease

描述(申请人提供)：亨廷顿病(HD)是一种遗传性神经退行性疾病，由亨廷顿蛋白(HTT)中的多聚谷氨酰胺(PolyQ)异常扩张引起，导致进行性痴呆、运动障碍和精神异常。目前，HD仍然没有治愈的方法。在HD中，纹状体和皮质神经元以一种未知的机制选择性死亡。迫切需要科学突破来揭开突变的HTT是如何导致神经元死亡的。新的证据表明，线粒体功能障碍在HD的发病机制中起着核心作用。但是，线粒体在HD中究竟是如何受损的仍不清楚。线粒体是能够迁移、分裂(经历分裂)和融合的动态细胞器。线粒体的分裂和融合是由具有竞争性活动的动力蛋白相关的GTP酶编排的。在正常情况下，线粒体在神经元中形成索状细丝，允许有效的能量传递、代谢产物的混合、钙缓冲和mtDNA突变的沉默。在这里，我们将检验这一新的假设，即持续性线粒体分裂是否代表了HD发病机制中线粒体功能障碍的机制基础。我们将解决以下问题：(1)突变的HTT是否会触发线粒体的持续分裂，进而导致线粒体的超微结构损伤、能量缺乏、线粒体呼吸功能受损、ROS产生、钙稳态异常以及线粒体DNA丢失？(2)突变的HTT是否招募并激活线粒体的分裂机制？(3)线粒体的分裂在突变的HTT诱导的神经变性和细胞死亡中是否起因果作用？为了回答这些问题，我们将分离初级纹状体或皮质神经元。此外，我们将使用突变的HTT转基因小鼠和死后HD脑组织。我们将使用跨学科和先进的技术来分析它们，包括3D时间流逝成像、EM断层成像、分子遗传学、药理学、生物化学和生物能量学。我们还将开发新的算法，通过3D时间推移成像来量化线粒体分裂和mthtt聚集体的形成。这项研究将提高我们对突变的HTT如何触发神经元死亡的基本理解。本研究的结果可能为HD和其他多Q病的代谢和线粒体缺陷提供新的机制基础。最重要的是，这项研究可能会为克服HD患者进行性神经元丢失的有效治疗带来新的希望，从而使患者能够改善生活。

DESCRIPTION (provided by applicant): Huntington's disease (HD) is a hereditary neurodegenerative disorder and is caused by an abnormal polyglutamine (polyQ) expansion in the huntingtin (htt) protein, leading to progressive dementia, motor defects and psychiatric abnormalities. Presently, HD remains without cure. In HD striatal and cortical neurons die selectively by an unknown mechanism. Scientific breakthroughs are desperately needed to unravel how mutant htt causes neuronal demise. New evidence emerged indicating that mitochondrial dysfunction plays a central role in the pathogenesis underlying HD. But, exactly how mitochondria become injured in HD remains unclear. Mitochondria are dynamic organelles able to migrate, divide (undergo fission) and to fuse. Mitochondrial fission and fusion is choreographed by dynamin-related GTPases with competing activities. At normal conditions mitochondria form cable-like filaments in neurons, allowing efficient energy transmission, mixing of metabolites, Ca2+ buffering, and silencing of mtDNA mutations. Here, we will test the novel hypothesis whether persistent mitochondrial fission represents a mechanistic basis for the mitochondrial dysfunction implicated in HD pathogenesis. We will address the following questions: (1) Does mutant htt trigger continuous mitochondrial fission, which in turn results in ultrastructural damage of mitochondria, energy deficits, impaired mitochondrial respiration, ROS production, abnormal Ca2+ homeostasis, and mtDNA loss? (2) Does mutant htt recruit and activate the mitochondrial fission machinery? (3) Does mitochondrial fission play a causal role in mutant htt-induced neurodegeneration and cell death? To answer these questions we will isolate primary striatal or cortical neurons. Additionally, we will employ mutant htt transgenic mice and postmortem HD brain tissue. We will analyze them using interdisciplinary and advanced techniques including 3D timelapse imaging, EM tomography, molecular genetics, pharmacology, biochemistry, and bioenergetics. We will also develop new algorithms to quantify mitochondrial fission and mthtt aggregate formation by 3D time-lapse imaging. This study will improve our basic understanding of how mutant htt triggers neuronal demise. Results obtained here may offer a new mechanistic basis for the metabolic and mitochondrial defects underlying HD and perhaps other polyQ disease. Most importantly, this study may bring new hopes for effective treatments to conquer progressive neuron loss in HD, so patients can lead improved lives.